As is generally known in the art, a hybrid electric vehicle utilizes an internal combustion engine and a battery power source together. The hybrid electric vehicle efficiently combines a torque of the internal combustion engine and a torque of a motor.
Hybrid electric vehicles may be divided into a hard type and a mild type according to power sharing ratio between an engine and a motor. In the case of the mild type of hybrid electric vehicle (hereinafter referred to as a mild hybrid electric vehicle), a mild hybrid starter & generator (MHSG) configured to start the engine or generate electricity according to an output of the engine is used instead of an alternator. In the case of the hard type of hybrid electric vehicle, a driving motor configured for generating driving torque is used in addition to an integrated starter & generator (ISG) configured to start the engine or generate electricity.
The MHSG may assist torque of the engine according to running states of the vehicle and may charge a battery (e.g., 48 V battery) through regenerative braking. Accordingly, fuel efficiency of the mild hybrid electric vehicle may be improved.
The mild hybrid electric vehicle includes a starter and the MHSG used as motors for starting the engine. When the engine is started by the starter on a road of which gradient is very high, there has been a problem in that a time required to start the engine is increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.